Mobile telephones and other portable electronic devices increasingly include a locating feature that enables a current geographic location of the devices to be either displayed on the devices or transmitted to a remote receiver. These features are generally called location services (abbreviated as LCS, for “LoCation Services”). LCS features that display location coordinates on a device are useful, for example, to device users who need to know where they are located relative to geographic map coordinates. Thus, LCS features can enable a device user to initiate a location request where the device acts as a Global Positioning System (GPS) terminal. Also, location requests may be initiated by third parties and transmitted to a device over a wireless network. Such third party requests are useful in various circumstances. For example, mobile telephone networks may be able to improve network efficiency and provide better Quality of Service (QoS) and roaming rates to a mobile user if the network can periodically monitor a mobile telephone location. Also, emergency services can sometimes save lives by rapidly and accurately identifying where emergency phone calls have originated. Other useful location-based services and data that can be provided through portable electronic devices include maps, weather forecasts, traffic data and local news.
Various locating technologies can be used to determine the location of a portable electronic device. For example, GPS satellites can be used to identify a location anywhere in the world of some mobile telephones. Further, because mobile telephones are already operatively connected to land-based network stations, the stations can transmit GPS satellite orbit parameters and navigation data to mobile telephones to aid fast acquisition of GPS satellites when a mobile telephone first starts its GPS function. Thus Assisted GPS (AGPS) services are commonly used to incorporate better and more efficient location services into mobile telephones. Secure User Plane Location (SUPL) is a technology developed by the Open Mobile Alliance (OMA) that concerns the transfer of assistance data and positioning data between a portable electronic device and a location platform, and includes standards such as the Open Mobile Alliance Secure User Plane Location 2.0 Periodic Trigger standard. A “user plane” means that assistance data and positioning data are transmitted between the device and the location platform over a conventional wireless communication channel such as a General Packet Radio Service (GPRS) channel. User plane communications are thus distinguished from control plane communications where assistance data and positioning data are transmitted between a device and a location platform over a packet switched (PS) channel in a network.
Other SUPL applications include monitoring the position of one or more mobile devices from a remote location. For example, a dispatch center of a delivery company or a command station of an emergency response team may need to monitor the location of individuals or vehicles in the field. In such applications the dispatch center or command station is referred to as an LCS client, and monitored electronic devices are referred to as target SUPL Enabled Terminals (SETs). The LCS client receives location data concerning a SET indirectly through a SUPL location server.
A SUPL location server generally must be able to communicate directly with at least four overhead satellites to be able to calculate an accurate AGPS position of a SET. Where communications with fewer or no satellites is possible, such as indoors or in “urban canyon” environments, a SUPL server will employ an alternative positioning method, such as a cell-identification method. However, such an alternative positioning method may be unacceptably inaccurate for many applications.
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